The disclosure of Japanese Patent Application No. 2001-036021 filed on Feb. 13, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to vibration dampers to be attached to a subject member to damp vibration of the subject member, and more particularly to a pneumatically controlled vibration damper that is novel in construction and capable of regulating vibration damping characteristics thereof by utilizing pneumatic pressure, so that the vibration damper exhibits vibration damping effect corresponding to vibration to be damped.
2. Description of the Related Art
A dynamic damper of passive type is known as means for damping vibration excited in a subject member that is likely to be vibrated, such as a body of an automotive vehicle. The passive-type dynamic damper generally includes a mounting member to be attached to the subject member and a mass member elastically connected via an elastic support member so that the mass member is elastically supported by the mounting member. Recently, there have been proposed pneumatically operated active vibration dampers in an attempt to obtain an enhanced damping effect. A known example of such a pneumatically operated active vibration damper is disclosed in JP-A-10-169705, wherein a working air chamber is formed to apply oscillating force to the mass member on the basis of a change of an air pressure within the working air chamber, so that the mass member is positively oscillated to generate an oscillating force that acts on the subject member to offset or actively damp vibration excited in the subject member.
As well known in the art, the mass member and the elastic support member constitute a single vibration system that serves as a secondary vibration system with respect to the subject member served as a primary vibration system. In order to obtain an excellent vibration damping effect, these conventional passive-type and active-type vibration dampers may advantageously utilize resonance of their vibration systems constituted by the mass member and the elastic support member. For this reason, it is desirable to tune a natural frequency of the vibration system to a frequency band of vibration to be damped.
However, such conventional vibration dampers of passive type and active type may suffer from an inherent problem. Namely, since the natural frequency of the vibration system constituted by the mass member and the elastic support member is fixedly determined by a mass of the mass member and a spring constant of the elastic support member, the natural frequency of the vibration system is likely to deviate from the frequency band of the vibration to be damped, when the vibration to be damped varies. Thus, the conventional vibration dampers do not necessarily exhibit an excellent vibration damping effect with respect to vibrations having a plurality of frequency bands or over a wide frequency range.
It is therefore one object of the invention to provide a vibration damper that is novel in construction, and that is capable of controlling vibration damping characteristics thereof and exhibiting an excellent vibration damping effect with respect to vibrations having a plurality of frequency bands or over a wide frequency range.
It is another object of the present invention to provide a vibration damper that is simple in construction and compact in size, and that eliminates a need for assembling a specific actuator therein.
The above objects may be attained according to the following modes of the invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the present invention is not limited to the following modes or combinations of technical features, but may otherwise be recognized based on a principle of the present invention that described in the whole specification and drawings, or may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A pneumatically controlled vibration damper for damping vibration of a subject member as a primary vibration system, the vibration damper including: (a) a mounting member adapted to be fixed to the subject member; (b) a mass member disposed spaced apart from the mounting member and displaceable relative to the mounting member; (c) an elastic connector secured to the mounting member and the mass member for elastically connecting the mass member to the mounting member so that the elastic connector and the mass member cooperate to form a secondary vibration system; (d) a working air chamber partially defined by the elastic connector and closed from an external area; (e) an air passage connected to said working air chamber for regulating an air pressure in the working air chamber from said external area; and (f) a static pressure-regulating system operable for substantially statically regulating the air pressure in the working air chamber via the air passage, so as to induce a substantially static elastic deformation of the elastic connector for changing a spring characteristic of the elastic connector.
In the pneumatically controlled vibration damper constructed according to this mode of the invention, the air pressure in the working air chamber is statically changed so as to change the spring characteristic of the elastic connector. This makes it possible to change a natural frequency of a vibration system of the vibration damper that is constituted by the mass member as a mass component and the elastic connector as a spring component, and that serves as the secondary vibration system. Described in detail, the vibration damper may be arranged by way of example such that an amount of statically elastic deformation of the elastic connector is made smaller, as the pressure of the air in the working air chamber is made closer to the atmospheric pressure, resulting in a soft spring characteristic of the elastic connector. Thus, the natural frequency of the vibration system of the vibration damper is tuned to a low frequency band, for example. Namely, the vibration damper of this mode of the invention is capable of controlling a static air pressure in the working air chamber, making it possible to tune or change the natural frequency of the vibration system constituted by the mass member and the elastic connector so as to correspond to a frequency of the vibration to be damped, even in the case where the frequency of the vibration to be damped varies. Thus, the vibration damper of this mode of the invention is capable of exhibiting an excellent passive or active vibration damping effect with the help of a resonance of the vibration system of the vibration damper (i.e., the secondary vibration system).
Further, the spring characteristic of the elastic connector can be suitably changed or determined according to a substantially static pressure value applied to the working air chamber. This arrangement makes it possible to suitably adjust the spring characteristic of the elastic connector so as to correspond to the change of the frequency of the vibration to be damped. Therefore, the vibration damper of the present mode of the invention is capable of efficiently exhibiting an excellent vibration damping effect with respect to input vibration in a plurality of frequency bands or over a wide frequency range, because of the resonance effect of the vibration system constituted by the mass member and the elastic connector.
It should be appreciated that the phrase xe2x80x9csubstantially static elastic deformationxe2x80x9d of the elastic connector is interpreted to mean a state of the elastic deformation of the elastic connector in which the elastic connector is able to be held in a substantially constant attitude, provided no dynamic or periodic change of the air pressure in the working air chamber is taken into account, which is induced by means of another system, such as a dynamic pressure-regulating system that will be described later. For instance, there is a case where the elastic connector undergoes its elastic deformation whose amount slightly continuously varies, and the variation in the amount of the elastic deformation of the elastic connector is small enough to ignore with respect to an amount of oscillating displacement of the elastic connector induced upon application of a vibrational load to the vibration damper or upon application of an active dynamic or periodic air pressure change to the working air chamber by means of the dynamic pressure-regulating system. In this case, such a slight variation in the amount of elastic deformation of the elastic connector needs not to be taken into account, so that it can be considered that the elastic connector undergo substantially static elastic deformation. Further, the static pressure-regulating system of the vibration damper of this mode of the invention is able to bring the elastic connector into a variety of states of its substantially static elastic deformation including its initial state, by applying substantially static air pressure of different levels to the working air chamber. In this respect, the substantially static air pressure applied to the working air chamber includes a dynamic or periodic air pressure change at a significantly high frequency in comparison with frequencies of vibration to be damped and frequencies of the dynamic air pressure change applied to the working air chamber by means of the dynamic pressure-regulating system. Namely, if such a dynamic air pressure change having the significantly high frequency is applied to the working air chamber, the elastic connector is not able to be elastically deformed according to the dynamic or periodic air pressure change induced in the working air chamber, resulting in the substantially static elastic deformation of the elastic connector. In the case where the static pressure-regulating system is operated to apply the dynamic air pressure change having the significantly high frequency to the working air chamber, as described above, it is further possible to regulate the level of the substantially static air pressure applied to the working air chamber, in other words, the spring characteristic of the elastic connector, by suitably regulating a duty ratio of the dynamic or air pressure change, for example.
According to the present mode (1) of the invention, the air pressure in the working air chamber is substantially statically regulated for permitting a static change of the spring characteristic of the elastic connector. This air pressure in the working air chamber may be statically regulated by alternately exposing or connecting the working air chamber to the atmosphere and a negative or positive pressure having a given constant value, or alternatively by changing the air pressure in the working air chamber among a plurality of given different pressure values or among suitable pressure values selected from continuously changing pressure values. A material for the elastic connector employed in the vibration damper of this mode of the invention may preferably be selected from the group consisting of various kinds of known rubber materials, elastomers, composite materials consisting of a rubber material and a canvas or a synthetic resin material. The shape, size and material of the elastic connector may be desirably determined taking into account a required characteristic of the elastic connector and the shapes of the mounting member and the mass member.
(2) A pneumatically controlled vibration damper according to the above mode (1), wherein the static pressure-regulating system is operable to substantially statically change the air pressure in the working air chamber by applying a substantially static air pressure having a pressure value selected from a predetermined range according to a frequency of the vibration to be damped so that a spring characteristic of the elastic connector become harder as a frequency of the vibration to be damped become higher. According to this mode of the invention, a natural frequency of the secondary vibration system, i.e., a vibration system of the vibration damper is made higher as the frequency of the vibration to be damped becomes higher. Thus, the vibration damper of this mode of the invention is capable of exhibiting an excellent active or passive vibration damping effect with the help of resonance effect of the secondary vibration system.
(3) A pneumatically controlled vibration damper according to the above-indicated mode (1) or (2), wherein the static pressure-regulating system is operable to apply to the working air chamber a substantially static air pressure whose value is changed between or among a predetermined different static pressure values according to a change in a frequency of the vibration to be damped so that the spring characteristic of the elastic connector is gradually changed. In the vibration damper constructed according to this mode of the invention, the natural frequency of the vibration system can be changed with high accuracy so as to follow the change in the frequency of the vibration to be damped, Thus, the vibration damper of this mode of the invention is able to exhibit a high vibration damping effect by effectively utilizing resonance of the vibration system thereof (i.e., the secondary vibration system).
(4) A pneumatically controlled vibration damper according to any one of the above-indicated modes (1)-(3), further comprising at least one abutting projection formed on an inner surface of the working air chamber such that the at least one abutting projection protrudes at least from one toward an other of said elastic connector and an abutting portion of said inner surface of said working air chamber, said working air chamber being opposed to the elastic connector, wherein the static pressure-regulating system is operable to regulate the air pressure in the working air chamber so that the abutting projection is brought into abutting contact with the elastic connector or the abutting portion of said inner surface of said working air chamber for applying a restricting force to the elastic connector. In the vibration damper according to this mode of the invention, the at least one abutting projection may be alternately brought into two operating states, namely an abutting state where the abutting projection is held in abutting contact with the elastic connector or the abutting portion of the inner surface of the working air chamber, and a non-abutting state where the abutting projection is spaced apart from the elastic connector or the abutting portion of the inner surface of the working air chamber, thereby alternatively providing a restricted or a non-restricted state of the elastic connector, for example. This arrangement makes it possible to change greatly and clearly the spring characteristic of the elastic connector with high stability.
The abutting projection may be arranged such that the abutting projection is brought into abutting contact with the elastic connector or the abutting portion of the inner surface of the working air chamber with a contact area that gradually increases with an increase in an amount of elastic deformation of the elastic connector. This arrangement makes it possible to gradually change the spring characteristic of the elastic connector by gradually increasing the restricting force applied to the elastic connector by means of the abutting projection, for example. Preferably, the abutting projection is disposed coaxially or concentrically with the elastic connector, and extends continuously or discontinuously about an elastic center axis of the elastic connector so as to be formed in a generally annular shape. This allows the elastic connector to be elastically deformed with high stability, when the abutting projection is held in its abutting state, whereby the elastic connector exhibits its desired spring characteristic with high stability.
(5) A pneumatically controlled vibration damper according to any one of the above-indicated modes (1)-(4), wherein the mounting member and the mass member are opposed to and spaced apart from each other in a vibration input direction in which the vibration damper primary receives a vibrational load to be damped, wherein the elastic connector comprises a connecting elastic body that extends outwardly from the mounting member in a direction perpendicular to the vibration input direction and is bonded at an outer peripheral portion thereof to the mass member so that the connecting elastic body primary undergoes shear deformation thereof upon a displacement of the mass member in the vibration input direction, and wherein the working air chamber is disposed between a surface of the mass member and a surface of the connecting elastic body that is opposed to the surface of the mass member in the vibration input direction. In the vibration damper according to this mode of the invention, the connecting elastic body is disposed in the vibration damper with its principle elastic axis conforming to the vibration input direction in which the vibrational load to be damped is applied, thereby increasing a spring ratio of the connecting elastic body. This arrangement enables a stable oscillation of the mass member in the vibration input direction, so that the vibration damper of this mode of the invention exhibits a desired vibration damping effect with high stability.
(6) A pneumatically controlled vibration damper according to any one of the above-indicated modes (1)-(5), wherein said air passage is formed through said mounting member. This arrangement makes it possible to fixedly form the air passage for applying a suitable air pressure to the working air chamber through the mounting member with simple structure and with effective utilization of the mounting member.
(7) A pneumatically controlled vibration damper according to any one of the above-indicated modes (1)-(6), wherein the vibration damper is applied to a vibration damper for an automotive vehicle, and a natural frequency of the secondary vibration system constituted by the elastic connector and the mass member is tuned to a low frequency band corresponding to engine idling vibration when the static pressure-regulating system operates to apply an atmospheric pressure to the working air chamber, and to a high frequency band corresponding to booming noises when the static pressure-regulating system operates to apply a static air pressure other than the atmospheric pressure to the working air chamber. The vibration damper according to this mode of the invention is capable of exhibiting excellent vibration damping effects with respect to both of the idling vibration to be damped during an idling condition of the vehicle and the booming noises to be damped during a running condition of the vehicle.
(8) A pneumatically controlled vibration damper according to any one of the above-indicated modes (1)-(7), further comprising a dynamic pressure-regulating system that is operable to apply to the working air chamber a dynamic or periodic air pressure change having a frequency corresponding to a frequency of the vibration to be damped, so as to actively oscillate the mass member. In the vibration damper according to this mode of the invention, the mass member may be actively or positively oscillated at the frequency corresponding to the frequency of the vibration to be damped, by dynamically changing the air pressure in the working air chamber at the frequency corresponding to the frequency of the vibration to be damped. As a result, the oscillating movement of the mass member acts to offset or positively damp the vibration to be damped excited in the subject member. Thus, the vibration damper of this mode of the invention is capable of effectively exhibiting an active vibration damping effect with respect to vibration to be damped.
It is noted that the pneumatically controlled vibration damper of this mode of the invention is capable of changing the natural frequency of its vibration system including the mass member (i.e., the secondary vibration system) so as to correspond to the frequency of the vibration to be damped, by using the static pressure-regulating system. That is, the vibration damper of this mode is capable of effectively generating the oscillating movement of the mass member at a plurality of frequency bands or over a wide frequency range by means of the dynamic pressure-regulating system, with the help of resonance effect of the vibration system. Thus, the vibration damper of this mode of the invention is capable of exhibiting the active vibration damping effect with respect to the plurality of frequency bands or over the wide frequency range.
The dynamic pressure-regulating system may be effectively embodied by alternately connecting the working air chamber to two external air sources having different pressure values at a frequency corresponding to the frequency of the vibration to be damped. Preferably, the atmosphere is used as one of the two air sources, thus simplifying the structure of the dynamic pressure-regulating system.
(9) A pneumatically controlled vibration damper according to the above-indicated mode (8), wherein the dynamic air pressure change generated by the dynamic pressure-regulating system is applied to the working air chamber together with a substantially static air pressure change generated by the static pressure-regulating system. In the vibration damper according to this mode of the invention, both of the dynamic air pressure change and the static air pressure change can be applied to the working air chamber through the same air passage, thus simplifying the structure of an air piping system including the air passage. Preferably, the static and dynamic air pressure-regulating systems commonly utilize at least one same air source, thus further simplifying the overall air piping system including the air sources.
(10) A pneumatically controlled vibration damper according to the above-indicated mode (8) or (9), wherein the dynamic pressure-regulating system includes a first switch valve operable for alternately connecting the working air chamber to a vacuum source and the atmosphere at a frequency corresponding to a frequency of the vibration to be damped, and a first duty ratio regulating system operable for regulating a duty ratio of a control signal applied to the first switch valve according to the vibration to be damped, the first duty ratio regulating system changing a ratio of a time of connection of the working air chamber to the vacuum source, to a period of a switching operation of the first switch valve so as to regulate an amplitude of the dynamic air pressure change having the frequency corresponding to the frequency of the vibration to be damped, which is applied to the working air chamber. The vibration damper according to this mode of the invention is capable of applying to the working air chamber the dynamic or periodic air pressure change whose frequency and amplitude are easily and sophisticatedly controlled so as to corresponds to those of the vibration to be damped. Thus, the vibration damper of this mode is able to exhibit a further improved active vibration damping effect with respect to vibration to be damped.